PHP note 2.0--php variables, data types and transformations, operators, process controls

2.1 Variables in PHP:

Define variable: $ variable name = value;

Variable name: The first digit after $ begins with $ must be the letter $ second digit can be a letter, a number, or an underscore. The customary variable name has a practical meaning, the second word is capitalized after the first letter--the hump is named.

Pre-defined variables: Receive data variables in $_get data volume is small, unsafe, via HTTP GET method to pass data

$_post data volume, security, through the HTTP POST way to pass data

$_request $_get+$_post, low efficiency

$_files upload variable, upload file via HTTP Post

Session: $_cookie saving data on the client

$_session saving data on the server side

Environmental information for $_server systems

2.2 Data types in PHP8

Basic data type (scalar type):

String strings must be enclosed in double quotes "" or single quotes ". The two quotation marks differ: the code in "" is executed, and the code in "does not execute, output according to ordinary characters."

Integer decimal, octal, hexadecimal, without quotation marks.

Float type float

When Boolean-type Boolean is printed, TRUE returns 1,false return null.

Composite type

Arrays Array

Objects Object

Special types

Resource Resource

Null value NULL only declares unassigned variable, assigning "" value of variable, unset (variable name)

Var_dump return type and value

2.3 Data-type conversions (implicit conversions)

Convert to Boolean:true--->1;

The following is converted to false when operating:

0 or 0.0----->false

Null character, empty array, null value----->false

Convert to Numeric type: true--->1,false---->0

Strings with E or e are converted to floating-point types.

Convert to String: null----> ""

Array----> "Array"

Object----> "Object"

Resource----> "resource# serial number"

2.4 operator

string concatenation: stitching symbol.

Arithmetic operators: +-*/%

Assignment: = + = = *=/=%=. =

Self-increment decrement operator: $i + + $i--to participate in the operation, in addition minus + + $i--$i first plus minus, then participate in the operation

Comparison operators:< > >= <= = = equals, compare values = = = identically, compare values and type! =! = = <>

Logical operators: X&&y x| | Y!x

Note: positive integers! Negative integer------>false!0------>true

The non-empty string--->false! " 0 "----->true!" 0.0 "----->false

Non-target operator: expression? True execution: false execution

2.5 Process Control

If

if (condition 1) {

Condition 1 is true when executed

}elseif (condition 2) {

Condition 2 is true when executed

}......

else{

The above conditions are not established, the implementation

}

Switch

Switch () {

Case Val: Execution code;

Case Val: Execution code;

Case Val: Execution code;

......

Default: The above conditions are not established when the implementation;

}

Difference: If can be nested, switch not.

PHP note 2.0--php variables, data types and transformations, operators, process controls